Executive processes are frequently implicated as a factor contributing to age-related cognitive deficits, and to cognitive impairments associated with a variety of different diseases and neuropathological conditions. However, it is not yet known whether variables hypothesized to reflect executive processes represent a unitary dimension of individual differences, if and how executive processes are related to other types of cognitive variables, and to what extent age-related effects on different cognitive variables may be mediated by age- related effects on executive processes. These issues will be investigated in a series of studies involving samples of between 100 and 250 healthy adults between 18 and approximately 80 years of age. The initial age-comparative studies will focus on four aspects of executive processes (i.e., updating, time-sharing, and planning), with each young and old adult participant performing three tasks hypothesized to assess each executive process aspect. The goals of these studies are to examine the degree to which the three variables postulated to represent the same aspect of executive processes are correlated with one another, and hence may represent a unitary dimension of individual differences, and to investigate possible changes in the pattern of correlations, and reliabilities of the executive process variables, across two sessions of practice. The final study in the project will involve a total of about 250 healthy adults ranging from 18 to 80 years of age who will perform a battery of tasks designed to assess different aspects of executive processes and other types of cognitive functioning such as perceptual speed and working memory. A variety of correlation-based analyses, including structural equation models, will be used to evaluate the plausibility of hypotheses regarding the unitary or multiple nature of executive processes, relations of executive process variables to variables representing other types of cognition, and the level (i.e., specific to individual variables or common to many variables) at which age-related influences operate on executive process variables.